1. Field of the Invention
This invention relates to a stratified burning internal combustion engine provided with a combustion chamber and intake ports, which are both suited especially for stratified burning.
2. Description of the Related Art
Stratified burning internal combustion engines are known for many years. To permit operation at low fuel consumption, a layer of a rich air-fuel mixture is formed in a combustion chamber and this fuel-rich layer is ignited. This makes it possible to ignite an air-fuel mixture having a large air/fuel ratio as a whole.
As one example of such stratified burning internal combustion engines, a stratified burning internal combustion engine in which stratified vertical tumble flows, that is, vertical vortices (hereinafter simply referred to as "tumble flows") are formed has already been commercialized as illustrated in FIGS. 34 and 35.
FIGS. 34 and 35 show the structure of one of cylinders of a 2-intake-port internal combustion engine, in which there are illustrated a cylinder block 322, a cylinder 324, a piston 326, a cylinder head 328 and a combustion chamber 330. Designated at numeral 334 is an upper wall of the combustion chamber 330. The upper wall 334 is shaped in the form of a pentroof which has inclined walls 334a,334b. Intake ports 340,342 are open through the inclined wall 334a of the combustion chamber 330 and are each provided with an intake valve 358. Incidentally, numeral 347 indicates an exhaust port arranged in communication with an exhaust passage 360, while numeral 359 designates an exhaust valve.
Intake air, which has flowed into the combustion chamber 330 through the respective intake ports 340,342, then flows along the inclined wall 334b toward an inner wall of the cylinder 324, said inner wall being located on extensions of axes of the individual intake ports 340,342, whereby tumble flows are formed in the combustion chamber 330 as indicated by arrows Fa,Fm.
As is depicted in FIG. 34, only one of the intake ports, namely, the intake port 342 is provided with an injector 312. A spark plug 310 is arranged adjacent to the intake valve 358 in the intake port 342 which is provided with the injector 312. In the vicinity of the spark plug 310, there is accordingly formed the tumble flow Fm of an air-fuel mixture which has been formed of inducted air and fuel injected from the injector 312, so that stratified tumble flows consisting of the tumble flow Fm of the air-fuel mixture and the tumble flow Fa of air are formed in the combustion chamber 330.
Even when the ratio of the air to the fuel inside the combustion chamber 330 is high, in other words, even upon lean burn in which the fuel concentration is low as a whole inside the combustion chamber 330, stable combustion is still feasible owing to the existence of an air-fuel mixture richer in fuel than those present at places remote from the spark plug 310, around the spark plug 310.
In the internal combustion engine shown in FIGS. 34 and 35, however, it is difficult to arrange two exhaust ports instead of the single exhaust port 347 because the spark plug 311 is disposed at the position corresponding to the tumble flow Fm formed by the intake port 342. A limitation is therefore imposed on the ability of exhaustion from the combustion chamber 330.
A stratified burning internal combustion engine permitting the arrangement of plural exhaust ports per cylinder has been being under development at the assignee company of the present application (U.S. patent application Ser. No. 07/946,476). The stratified burning internal combustion engine under development will now be described in short with reference to FIGS. 34 and 35. A spark plug is centrally disposed on a ceiling of a combustion chamber. Intake ports are each provided with a partition so that an interior of each intake port is divided into two passages. Among the thus-formed passages of these intake ports, only those closer to the spark plug are fed with fuel. This makes it possible to form a tumble flow of a richer air-fuel mixture around the spark plug. According to the stratified burning internal combustion engine so constructed, the spark plug is disposed centrally on the ceiling of the combustion chamber so that plural exhaust ports can be easily arranged for the exhaustion of the combustion chamber.